The present invention relates to novel mixed oxides for tunable lasers. More specifically it relates to mixed oxides having a crystal field such that the tunable emission covers the wavelength range from to 1.8 .mu.m.
In order to obtain tunable solid lasers it is known to use ions of transition metals such as Cr.sup.3+, V.sup.2+, Ni.sup.2+ and Co.sup.2+ as doping ions in oxides such as MgO and BeAl.sub.2 O.sub.4 and fluorides such as MgF.sub.2, ZnF.sub.2 and KZ.sub.n F.sub.3. Thus, the article "Tunable alexandrite lasers", by Walling et al. in IEEE. J. Quantum Electron, vol. QE-16, no. 12, pp. 1302-1314, 1980 illustrates solid lasers tunable in the range 0.7 to 0.82 .mu.m obtained by doping BeAl.sub.2 O.sub.4 by Cr.sup.3+. The article entitled "Broadly tunable cw operation of Ni: MgF.sub.2 and Co: MgF.sub.2 lasers" by P. F. Moulton et al. in Appl. Phys. Letter, vol. 35, 11, p. 838-840, 1979, shows that it is possible to obtain lasers tunable in the ranges 1.61 to 1.74 .mu.m and 1.63 to 2.08 .mu.m by doping MgF.sub.2 respectively by Ni and Co.
Lasers tunable in the range 1.85 to 1.05 .mu.m are also known, which are formed from KZnF.sub.3 doped by Co.sup.2+, as described in "CW IR laser action of optically pumped Co.sup.2+ : KZnF.sub.3 " by W. Kunzel et al., Optics Communications, vol. 36, no. 5, pp. 383-386 (1981).
Thus, none of the materials referred to hereinbefore makes it possible to cover the wavelength range between 1.1 and 1.6 .mu.m which is of interest, e.g. for the spectroscopic study of semiconductor quaternary alloys of the InGaAsP type. Other materials suitable for this application are known and these are MgF.sub.2 : V.sup.2+ and MgO: Ni.sup.2+ which respectively cover the range 1.05-1.3 .mu.m and 1.3 to 1.4 .mu.m (cf. Appl. Phys. Lett. 35, p. 838, 1979).
However, the use of such materials suffers from certain difficulties. Thus, if it is wished to use MgF.sub.2 : V.sup.2+, it is difficult to stabilize vanadium in valence 2 and any residual ion in another valence state acts as a poison, which reduces the emission yield.
Moreover, the V.sup.2+ in MgF.sub.2 has a diagram of energy levels such that the laser emission is reabsorbed as from the excited level emitting the laser effect. In addition, products containing V.sup.2+ in fluoric matrixes are difficult to use.
In the case of MgO: Ni.sup.2+, the main difficulty is in the production of said product in the form of monocrystals, because its melting point is very high, at approximately 3000.degree. C. It is also difficult to obtain monocrystals of sufficient size and good optical quality for conventional pulling procedures, e.g. using the Czolchralski method.